Efficient cache invalidation schemes for mobile data accesses

Identical data may cause many problems in all types of databases, specially distributed and replicated databases. These data will attack consistency and redundancy which are two important problems in databases. Databases or replicas may contain similar records with different appearance, concerning the same real word entity because of many reasons. Some of these reasons are: Entry errors, unstandardized abbreviations, differences details of various databases schemas, package lost, noisy environments and etc are some reasons of duplicates. This paper proposes an approach to detect duplicate or similar data, which are faulty or noisy so they are distinguished as different data, among various replicas in distributed or replicated databases. Multi criteria decision making algorithm is employed for this propose. To detect identical records, at first step some priorities are defined for fields and then percent of similarity of records evaluate. Algorithm's time overhead is improved through using special order of priorities. Multi criteria decision making algorithm is used to decide how to combine records with each other and which record is complete and true one. An instance based learning approach is employed to learn how to set priorities for various fields, creating a uniform schema and find their appropriate match, in other replica

An Algorithm for Detecting Similar Data in Replicated Databases Using Multi Criteria Decision Making

With the tremendous growth of the portable computing devices and wireless communication, the mobile computing has become extremely popular. The wireless enabled portable computing devices with massive storage capacity and high-end processing capabilities have started to make the extensive use of mobile databases already. The rising popularity in these computing paradigms demands that the mobile computing be reliable enough to ensure the continuous data availability and integrity. However mobility comes at the cost of bandwidth, limited power, security and interference. In modern mobile computing systems data replication has been adopted as an efficient means to ensure the data availability and integrity as well as an effective means to achieve the fault tolerance. Data replication not only ensure the availability of the data but also reduce the communication cost, increase data sharing and increase the safety of the critical data. Furthermore, it also determine when and where (location) to place the replica of data, controlling the number of data replicas over a network for efficient utilization of the network resources. In this study we survey the research work in data replication for mobile computing. We reviewed some of the existing data replication techniques proposed by the research community for mobile computing environment for efficient management of data replicas.

Review of Data Replication Techniques for Mobile Computing Environment

In the diagnosis researches on the implementation status of construction engineering projects (CEP), two major problems remain unsolved yet by far. On one hand, there is not a scientific approach to extract and determine the diagnosis indicators for the implementation status. On the other hand, it still lacks an effective method to analyze and diagnose the implementation status. As an improvement, in this paper these two problems are studied respectively. According to the three required conditions for the implementation status diagnosis, the determination approach based on quantitative scoring for the index setup is firstly presented. All of the indicators are transformed and standardized into the range value forms within [0,1]. Then, the recursive analysis method and model of the diagnosis indicators, which combines the model-based method together with the characteristic based method at the meantime, is proposed, and the grading judgment standards for the implementation status of CEP are presented based on the windage principle. Finally, an indemnificatory housing project which contains 21 residential buildings is taken for a case study to validate the proposed method. It is shown that the proposed method is able to effectively obtain the actual implementation status of large-scale construction projects and find out the exact problems as well as the targeted measures.

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A Diagnosis Method of Implementation State Management in Large-Scale Construction Projects

Mobile technology is going to be one of the most useful and practical technologies over 21 century. Mobile devices with integrated databases or caches are so useful for most of applications. This new environment with mobile servers and clients has some special characteristics that vary it from traditional distributed systems. Because of these special properties, protocols which were designed for traditional systems are not suitable for mobile environments. Previous schemes are passive in nature and rarely consider these new characteristics. One of the most important and useful schemes especially in distributed databases is replication. Replication techniques are used to increase performance, availability, reliability and scalability of various types of distributed systems (e.g. p2p and data grid). But obviously they are not appropriate for this new environment with unique characteristics and dynamic features. It is better to design situation depended protocols with dynamic nature. In this paper we illustrate part of a framework that can mange replication strategy in various situations. For this mean values of most important properties for basic components of environment (e.g. mobile servers and clients) will be used to choose an appropriate strategy through multi criteria decision making approach.

Detecting appropriate replication approach considering client and server parameters in mobile environment

Caching can reduce expensive data transfers and improve the performance of mobile computing. In order to reuse caches after short disconnections, invalidation reports are broadcast to clients to identify outdated items. Detailed reports may not be desirable because they can consume too much bandwidth. On the other hand, false invalidations may set in if the accurate timing of updates is not provided. In this research, we aim to reduce the false invalidation rates of cached items. Based on our analysis, false invalidation rates are closely related to clients' reconnection patterns (i.e., the distribution of the time spans between disconnections and reconnections). We show that in theory for any given reconnection pattern, a report with a minimal false invalidation rate can be derived. For practical uses, we propose to capture the reconnection pattern by sampling and develop a method to compose a near-optimal invalidation report. This method is simple and fast. Experimental results have confirmed that our method is indeed more effective in reducing the false invalidation rate than others.

http://delab.csd.auth.gr/~dimitris/courses/mpc_fall05/papers/invalidation/ACM_MDM_05_near_opt_invalidation_reports.pdf

Chih-Fang Wang

Papers

An approach of composing near optimal invalidation reports